1. Field of the Invention
The present invention relates to a high pressure fuel pump and a seal system using therefor.
2. Description of the Conventional Art
As illustrated in FIG. 11, a conventional high-pressure fuel pump has a rubber type oil seal 52 slidably arranged on the outer peripheral side of a plunger (axle) 51, and this oil seal 52 separates and seals two liquids of gasoline (fuel) G and engine oil (lubricating oil) O. Further, this high-pressure fuel pump has a return pipe 54 at a cylinder (housing) 53, in order is to return the gasoline G, which is slightly leaked from a portion between the plunger 51 and the cylinder 53 as a bearing of the plunger 51, to a fuel tank (refer to Unexamined Japanese Patent Publication No. 8-68370 (FIG. 2)).
In the above-described high-pressure fuel pump, earnest works has been carried out to omit a gasoline recovering circuit by the return pipe 54 in order to simplify a structure. However, when the gasoline recovering circuit is omitted, the gasoline G leaked from a portion between the plunger 51 and the cylinder 53 is retained as it is so that the pressure may become equal to discharge pressure (about 10 MPa). Under such high pressure, the oil seal 52 may be damaged at an early stage. In order to prevent this problem, a pipe for connecting from a fuel pump to a suction port of the high-pressure fuel pump is distributed to a return port so as to make the pressure applied to the oil seal 52 to be a lowest pressure of the fuel pump (about 0.5 MPa). However, even this pressure still affect to the oil seal 52 not small. Further, the plunger 51 reciprocates at a remarkably high speed according to the work of an engine.
However, a single product of an oil seal that is usable under severe conditions of “high speed”, “high pressure” and “fuel resistance” has not developed yet, and thus it is required to develop a new seal system that is usable under such the severe conditions.